The Environmental Protection Agency yesterday abandoned its push to revise two air-pollution rules in ways that environmentalists had long opposed, abruptly dropping measures that the Bush administration had spent years preparing.

....The proposal on parks would have changed the rules for new plants being built nearby....Clean-air advocates had protested that this might allow parks such as Virginia's Shenandoah  where the famous mountaintop views are already obscured by smog and haze  to become even dirtier on certain days.

....The other rule dealt with the agency's New Source Review process, which dictates when existing power plants must implement additional pollution-control measures....John Walke of the Natural Resources Defense Council, an environmental advocacy group, said the rule would have allowed plants to operate for longer hours and produce more overall pollution.

"I am stunned. I've been fighting these dirty rules for years," Walke said. "And within the span of an hour," he said, both were suddenly moot.

It's not clear what prompted this about face. But it's welcome news regardless.